An aqueous solution (100 mL) of potassium hydroxide (32.7 g, 0.58 mol) was slowly added to an acetone solution (500 mL) of 4-nitro-1H-pyrazole (30 g, 0.27 mol) under stirring at room temperature. After 30 minutes of reaction, an acetone solution (100 mL) of 2-bromoacetic acid (38.7 g, 0.27 mol) was added dropwise. The reaction mixture was continued to be stirred overnight. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was diluted with water and extracted three times with ethyl acetate, the organic phases were combined and concentrated under reduced pressure. Subsequently, the residue was further extracted with a solvent mixture of dichloromethane and methanol, and the organic phases were combined and concentrated again under reduced pressure to give the target product 2-(4-nitro-1H-pyrazol-1-yl)acetic acid (40 g, 88% yield).
